Patent Application
20140022303
1. Field of the Invention
The present invention relates to an inkjet recording apparatus and an inkjet recording method for recording an image on a recording medium by using an inkjet recording head.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2005-178378 describes a full-line inkjet recording apparatus that includes a recording head and a conveying mechanism for conveying a recording medium. In the recording head, nozzle arrays (chips), each having a plurality of nozzles, are arranged in a staggered manner. The full-line inkjet recording apparatus performs recording over the entire width of a recording medium.
In general, overlapping portions exist in a full-line recording apparatus, because a plurality of chips are arranged in a staggered manner. The overlapping portions perform recording using two chips. Therefore, if the density balance between the two chips is not correct, the density of an image formed by these chips may become non-uniform, which reduces the quality of the image. Such a non-uniform density may be inconspicuous for a monochrome image. However, if the overlapping portions are disposed at the same position for different colors, an imbalance in the density is exaggerated and easily recognized as a non-uniform density.
In contrast, in the recording apparatus describe in Japanese Patent Laid-Open No. 2005-178378, the overlapping portions for different colors are separated from each other in the nozzle array direction, so that the effect of a non-uniform density described above is reduced.
However, in order to avoid overlapping of the recording heads for all colors, the length of the recording heads is increased in the nozzle array direction, which may increase the size of the recording apparatus.
According to a first aspect of the invention, an inkjet recording apparatus includes a recording unit configured to perform recording by moving recording heads each corresponding to one of a plurality of colors relative to a recording medium and by ejecting inks having the plurality of colors from the recording heads, the plurality of colors including a first color, a second color, a third color, and a fourth color, the recording heads each including a plurality of nozzle arrays that are arranged so as to be displaced from each other in an array direction of nozzles so that the nozzle arrays have an overlapping portion in an intersecting direction that intersects the array direction, wherein a proportion of colors recorded by using the first color ink and the second color ink to colors that are recordable by the inkjet recording apparatus is lower than a proportion of colors recorded by using the third color ink and the fourth color ink to colors that are recordable by the inkjet recording apparatus, and wherein a width with which the overlapping portion of the recording head for the first color and the overlapping portion of the recording head for the second color overlap in the intersecting direction is larger than a width with which the overlapping portion of the recording head for the third color and the overlapping portion of the recording head for the fourth color overlap in the intersecting direction.
According to a second aspect of the invention, an inkjet recording apparatus includes a recording unit configured to perform recording by moving recording heads each corresponding to one of a plurality of colors relative to a recording medium and ejecting inks having the plurality of colors from the recording heads, the plurality of colors including a first color, a second color, a third color, and a fourth color, the recording heads each including a plurality of nozzle arrays that are arranged so as to be displaced from each other in an array direction of nozzles so that the nozzle arrays have an overlapping portion in an intersecting direction that intersects the array direction, wherein a sum of an amount of first color ink and an amount of second color ink used for colors that are recordable by the inkjet recording apparatus is smaller than a sum of an amount of third color ink and an amount of fourth color ink used for colors that are recordable by the inkjet recording apparatus, and wherein a width with which the overlapping portion of the recording head for the first color and the overlapping portion of the recording head for the second color overlap in the intersecting direction is larger than a width with which the overlapping portion of the recording head for the third color and the overlapping portion of the recording head for the fourth color overlap in the intersecting direction.
According to a third aspect of the invention, an inkjet recording method includes performing recording by moving recording heads each corresponding to one of a plurality of colors relative to a recording medium and ejecting inks having the plurality of colors from the recording heads, the plurality of colors including a first color, a second color, a third color, and a fourth color, the recording heads each including a plurality of nozzle arrays that are arranged so as to be displaced from each other in an array direction of nozzles so that the nozzle arrays have an overlapping portion in an intersecting direction that intersects the array direction, wherein a proportion of colors recorded by using the first color ink and the second color ink to colors that are recordable is lower than a proportion of colors recorded by using the third color ink and the fourth color ink to colors that are recordable, and wherein a width with which the overlapping portion of the recording head for the first color and the overlapping portion of the recording head for the second color overlap in the intersecting direction is larger than a width with which the overlapping portion of the recording head for the third color and the overlapping portion of the recording head for the fourth color overlap in the intersecting direction.
According to a fourth aspect of the invention, an inkjet recording method includes performing recording by moving recording heads each corresponding to one of a plurality of colors relative to a recording medium and ejecting inks having the plurality of colors from the recording heads, the plurality of colors including a first color, a second color, a third color, and a fourth color, the recording heads each including a plurality of nozzle arrays that are arranged so as to be displaced from each other in an array direction of nozzles so that the nozzle arrays have an overlapping portion in an intersecting direction that intersects the array direction, wherein a sum of an amount of first color ink and an amount of second color ink used for colors that are recordable is smaller than a sum of an amount of third color ink and an amount of fourth color ink used for colors that are recordable, and wherein a width with which the overlapping portion of the recording head for the first color and the overlapping portion of the recording head for the second color overlap in the intersecting direction is larger than a width with which the overlapping portion of the recording head for the third color and the overlapping portion of the recording head for the fourth color overlap in the intersecting direction.
According to the present invention, in a recording apparatus that includes recording heads each including a plurality of chips (nozzle arrays) that are arranged so as to overlap, an increase in the size of the recording apparatus is suppressed.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The present invention is applicable to an inkjet recording apparatus that performs recoding by moving a recording head, which ejects ink, relative to a recording medium. Hereinafter, the structure of a printer will be described in detail.
The sheet feeding unit 1 contains and feeds a rolled continuous sheet. The sheet feeding unit 1 contains two rolls R1 and R2, and feeds a sheet from one of the rolls R1 and R2 that is selected. Alternatively, the sheet feeding unit 1 may contain only one roll or more than two rolls. The decurling unit 2 reduces curling (warping) of a sheet that has been fed from the sheet feeding unit 1. The decurling unit 2 includes two pinch rollers and one driving roller. The decurling unit 2 warps the sheet in a direction opposite to curling of the sheet and pinches the sheet between the rollers so as to reduce the curling. The oblique sheet correction unit 3 corrects oblique conveyance (inclination with respect to the proper conveyance direction) of the sheet that has passed through the decurling unit 2. In the oblique sheet correction unit 3, an edge of the sheet to be aligned is pressed against a guiding member, so that the oblique conveyance of the sheet is corrected.
The printing unit 4 forms an image on the sheet using a recording head 14 while the sheet is being conveyed. The printing unit 4 includes a plurality of conveying rollers that convey the sheet. The recording head 14 is a full-line recording head, in which nozzles are formed so as to extend over the entire width of the sheet. A plurality of recording heads are arranged in the conveying direction. In the present embodiment, the recording heads for seven colors, including cyan (C), magenta (M), yellow (Y), light cyan (Lc), light magenta (Lm), gray (Gy), and black (Bk) are arranged. Ink may be ejected from the nozzles by using exothermic elements, piezoelectric elements, electrostatic element, or MEMS elements. Color inks are respectively supplied from ink tanks to the recording heads through ink tubes.
The inspection unit 5 optically reads a test pattern or an image printed on the sheet by the printing unit 4, and thereby inspects the state of nozzles in the recording head, the state of sheet conveyance, and the position of the image. The cutter unit 6 includes a mechanical cutter that cuts the sheet, which has being printed, into cut sheets having a predetermined length. The cutter unit 6 includes a plurality of conveying rollers for feeding the sheet to the next step. The information recording unit 7 records print-related information, such as a serial number of printing or the date of printing, on the back side of the sheet that has been cut. The dryer unit 8 dries the ink in a short time by heating the sheet that has been printed by the printing unit 4. The dryer unit 8 includes a conveying belt and a conveying roller for feeding the sheet to the next step.
The sheet winding unit 9 temporarily winds a continuous sheet, whose front side has been printed, when duplex printing is performed. The sheet winding unit 9 includes a winding drum for winding the sheet. When the front side has been printed, the continuous sheet is temporarily wound around the winding drum before being cut. After the sheet has been wound, the winding drum rotates in a reverse direction, and the sheet is fed to the decurling unit 2 and to the printing unit 4. Because the sheet has been reversed, the printing unit 4 can print the back side of the sheet. The duplex printing operation will be described in detail below.
The output/conveyance unit 10 conveys the sheet, which has been cut by the cutter unit 6 and dried by the dryer unit 8, to the sorter unit 11. When necessary, the sorter unit 11 sorts the printed sheets into groups and outputs the groups of sheets to different trays of the output tray 12. The control unit 13 performs the overall control of the printer.
When the controller 15 receives a signal from the external apparatus 16, the controller 15 generates recording data to be recorded on the sheet S using the recording head. The recording data is stored in the RAM 1503 as a print buffer. Moreover, the controller 15 transfers the data in the print buffer to a head driver 301. The head driver 301 converts the data into data for ejecting ink droplets using recording heads for different colors, and thereby performs a recording operation. The details of the image processing will be described below.
The controller 15 controls motor drivers, including a conveying system motor driver 302 and a detection system motor driver 303, so as to drive driving sources, such as a conveying motor 304 and a scanner motor 305, and thereby performs a sheet-conveying operation and a detection operation.
Next, the basic operation of printing will be described. Both the simplex printing operation and the duplex printing operation will be described, because these are not the same.
When the front surface printing sequence is finished, the back surface printing sequence is started. In the back surface printing sequence, first, the winding drum of the sheet winding unit 9 rotates in a direction opposite to the winding direction (clockwise in the figures). The leading end of the sheet (i.e., the trailing end of the sheet when the sheet was wound) is fed into the decurling unit 2. The decurling unit 2 performs decurling in a direction opposite to that of the previous decurling operation. This is because the sheet has been wound around the winding drum of the sheet winding unit 9 in a reversed manner compared with the time when the sheet was wound around the sheet feeding unit 1, and the sheet is curled in the opposite direction. Then, the sheet passes through the oblique sheet correction unit 3, and the printing unit 4 prints the back side of the continuous sheet. The printed sheet passes through the inspection unit 5, and the cutter unit 6 cuts the continuous sheet into cut sheets each having a predetermined length. The information recording unit 7 does not record print information on the cut sheet because both sides of the cut sheet have been printed. The cut sheets are individually conveyed to the dryer unit 8, passes through the output/conveyance unit 10, and successively output to and stacked on the output tray 12 of the sorter unit 11. Thus, the back surface printing sequence is finished.
Next, the structure of the printing unit 4 of the present embodiment will be described.
Regions X1 to X6, which are surrounded by dotted lines in
In
As can be seen from
Next, the reason for making the positions of the overlapping portions of the recording head 14K and the recording head 14Lc the same in the nozzle array direction in this embodiment will be described.
First, referring to
In step S1, multivalued image data is input to the printer. The multivalued image data is 8-bit RGB data. Next, in step S2, color processing A is performed. This is gamut mapping, which compresses and expands the multivalued image data to colors that are reproducible by the printer. In the color processing A, the input RGB data is converted to multivalued data for R′G′B′ that has been mapped.
In step S3, color processing B is performed. This is color separation processing, in which the converted data for R′G′B′ is converted to data for ink colors used by the printer. Because the present embodiment uses seven color inks, conversion from R′G′B′ to C, M, Y, Bk, Lc, Lm, and Gy is performed. In step S4, gradation correction is performed to correct the gradation characteristics of ink colors C, M, Y, Bk, Lc, Lm, and Gy. In the steps S2, S3, and S4, the conversion described above is performed using a lookup table.
In step S5, quantization is performed on the data whose gradation has been corrected for each ink color. To be specific, a generally used quantization method, such as error diffusion or dithering, is used. In step S6, the data that has been processed in steps S1 to S5 is supplied to the recording heads as signal values, sorted for recording, and allocated to the overlapping portions. Then, ink is ejected and recording is performed on a recording sheet.
In the color processing B of step S3, a lookup table, which contains one-to-one correspondence between the signal value for R′G′B′ and the signal value for the ink colors C, M, Y, Bk, Lc, Lm, and Gy, is used. An example of the correspondence between signal values for R′G′B′ and signal values for the ink colors is as follows.
Input values: R′=10, G′=10, B′=10
Output values: C=5, M=5, Y=5, Bk=220, Lc=0, Lm=0, Gy=20
The R′G′B′ signal values for white are converted to signal values for the ink colors M, Y, Bk, Lc, Lm, and Gy as follows.
Input values: R′=255, G′=255, B′=255
Output values: C=0, M=0, Y=0, Bk=0, Lc=0, Lm=0, Gy=0
When the color gradually changes from white to cyan, the output value first increases for the ink color Lc, and gradually shifts to the ink color C.
For cyan, the R′G′B′ signal values are converted to signal values for the ink colors C, M, Y, Bk, Lc, Lm, and Gy.
Input values: R′=0, G′=255, B′=255
Output values: C=255, M=0, Y=0, Bk=0, Lc=135, Lm=0, Gy=0
When the color changes form cyan to black, the complementary colors Lm and Y increase, and then Lm shifts to M. Meanwhile, Gray increases and finally reaches black.
In the present embodiment, light-colored inks (Lc, Lm) of relatively low density are used to improve graininess. These two inks are usually used for bright colors, and are rarely used simultaneously with Bk ink, which is used for reproducing dark colors. In
Recording heads for such inks that are not simultaneously used have the overlapping portions that are disposed at the same position in the nozzle array direction. Thus, the length of the recording heads in the nozzle array direction is reduced. That is, even if the positions of the overlapping portions are the same in the nozzle array direction, regions that are recorded by the overlapping portions for such inks, whose combination is not used, do not overlap. Therefore, the positions of the overlapping portions may be the same in the nozzle array direction. The specific structure of the recording head according to the present embodiment will be described below in detail.
For lines other than the white→cyan→black line, the frequency with which combinations of different color inks that are simultaneously used are examined as follows. The printer according to the present embodiment includes the recording heads for seven colors. Thus, the number of combinations of two different colors is twenty-one.
The frequency corresponds to the proportion of the number of colors for which two color inks are used to the number colors recordable by the printer (256×256×256). The proportion is obtained by counting, for all input signal values (RGB data) in step S1, the number of the input signal values for which the product of output signal values in step S5 are not zero. Because the output signal values in step S5 have been quantized, the product is not zero if and only if the signal values for the two colors are present, i.e., if the two colors are simultaneously used. Thus, by counting the number of the input signal values (RGB data) for which the above product is not zero, the frequency with which two different color inks are simultaneously used is obtained.
Referring back to
As can be seen from
As described above, for the recording heads for ink colors that are simultaneously used with a low frequency, the positions of the overlapping portions may be the same in the nozzle array direction.
In the present embodiment, the positions of the overlapping portions of the recording head for BK ink and the recording head for Lc ink are the same in the nozzle array direction. Thus, as illustrated in
In the description of the present embodiment using
In the description above, the overlapping portions of the recording heads 14M, 14Y, 14Gy, 14Lm, and 14Lc do not overlap at all in the conveying direction. However, parts (for example, several nozzles) of the overlapping portions may overlap. This is because, even if the colors are simultaneously used with a high frequency, when the overlapping portions overlap in a small region, non-uniform density occurs in the small region, whereby non-uniform density does not become conspicuous. The positions of the overlapping portions of the recording head 14K and the recording head 14Lc are the same in the nozzle array direction. However, parts of the overlapping portions may be disposed at different positions in the nozzle array direction.
According to the present invention, the width with which the overlapping portions for colors that are simultaneously used with a low frequency overlap each other in the conveying direction (a direction that intersects the nozzle array direction) is larger than the width (including zero width) with which the overlapping portions for colors that are simultaneously used with a high frequency overlap in the conveying direction. Thus, with the present invention, occurrence of non-uniform density is suppressed, and reduction in the length of the recording head in the nozzle array direction is realized. According to the present invention, it is assumed that the recording heads for a first color (for example, black) and a second color (for example, light cyan) that are simultaneously used with a low frequency and the recording heads for a third color (for example, cyan) and a fourth color (for example, yellow) that are simultaneously used with a high frequency are provided. The width with which the overlapping portions of the recording heads for the first color and the second color overlap in the conveying direction is larger than the width with which the overlapping portions of the recording heads for the third color and the fourth color overlap in the conveying direction.
Next, a second embodiment of the present invention will be described. The elements already described in the first embodiment will be denoted by the same numerals and the description of such elements will be omitted.
In the first embodiment and the modification of the first embodiment, the width with which the overlapping portions for colors that are simultaneously used with a low frequency overlap in the conveying direction is larger than the width with which the overlapping portions for colors that are simultaneously used with a high frequency overlap in the conveying direction. In contrast, in the present embodiment, the width with which the overlapping portions for colors, for which a small amount of ink is used when the colors are simultaneously used, overlap in the conveying direction is larger than the width with which the overlapping portions for colors, for which a large amount of ink is used when the colors are simultaneously used, overlap in the conveying direction. This is because, even when the frequency of with which color inks are simultaneously used is low, if the amount of inks simultaneously used is large, non-uniform density becomes conspicuous.
The amount of ink simultaneously used corresponds to the total amount of ink for the number of colors (256×256×256) recordable by the printer. For all input signal values (RGB data) in step S1, the sum of the output signal values in step S5 is calculated. The output signal value in step S5 has been quantized. Therefore, by multiplying the sum by the input signal values (RGB data), the number of dots that are simultaneously recorded, i.e., the amount of ink used when two different color inks are simultaneously used is calculated.
Combinations of inks that are simultaneously used with a comparatively small amount are as follows.
As described above, when the amount of ink simultaneously used is taken into consideration, disposing the overlapping portion for the Bk ink and the overlapping portions for the light-colored inks (Lc, Lm) at the same position or in a partially overlapping position in the nozzle array direction is effective. Therefore, as illustrated in
Next, a third embodiment of the present invention will be described. The elements already described in the first and second embodiments will be denoted by the same numerals and the description of such elements will be omitted. In the present embodiment, the positions of the overlapping portions of the recording heads for three colors are the same in the nozzle array direction.
Therefore, in the present embodiment, for the recording head 14K for Bk, the recording head 14Lc for Lc, and the recording head 14M for M, the positions of the overlapping portions are the same in the nozzle array direction. In this way, by making the positions of the overlapping portions of the recording heads for two or more colors be the same in the nozzle array direction, further reduction in the length of the recording head in the nozzle array direction is realized.
Some inkjet recording apparatuses use a high chroma ink having a so-called spot color or a special color, which is different from the process colors. Examples of such inks include an orange (Or) ink, a green (G) ink, and a blue (B) ink. These inks are used in a part of the color reproduction range, and are not simultaneously used with other inks. For a printer that uses such special colors, by overlapping the overlapping portion of the recording head for at least one of the special colors with the overlapping portion for the recording head for a color other than the special colors, the size of the recording head in the nozzle array direction may be reduced. In
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-139955 | Jun 2010 | JP | national |
This application is a continuation application of U.S. patent application Ser. No. 12/960,428 filed Dec. 3, 2010, which claims priority from Japanese Patent Application No. 2010-139955 filed Jun. 18, 2010, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12960428 | Dec 2010 | US |
| Child | 14039452 | US |
